Pulse modulating system



Oct. 14, 1952 J. BOISVIEUX ET AL 2,614,247

PULSE MODULATING SYSTEM Filed Dec. 22. 1948 F-lG. l.

II I: X /2 Additional Mixing Tube Circuit For Multiplex 7 Operation m ISource of Source of mgfulating unmoduluted v loge impulses INVENTORS J 5013 v/ uy M Patented Oct. 14, 1952 {UNITED STATE PULSE MODULATINGYSYSTEM Jacques Boisvi'eux, Nogent sur-Marne, and

Jacques Chaumeron, Paris, France, assignors to Societe FrancaiseSadir-Carpentierp Paris, France, a corporation of .France ApplicationDecember 22, 1948, Serial No.-66,644i l In France December 26, 1947 uOur invention has for its object the amplitude modulation of impulsesand it covers more particularly the production of impulses the amplitudeof which is a linear function of the modulating voltage within the totalrange of variation of the letter, said amplitude being capable ofsinking to zero.

ing such a modulation consists in sending unmodulated impulses to thecontrolling grid of a 'pentode tube, the suppressor grid of whichreceives the modulating voltage in addition to a suitable negative bias.It is thus possible to obtain an amplitude modulation of the impulse butthe amplitude of the impulse is not in this case alinear function of themodulating voltage, chiefly because the characteristic curve of apentode is not linear when the anode current approaches zero; as amatter of fact, said characteristic curve is such that the anode currentis a function of the voltage of the suppressor grid when the otherelectrodes are submitted to unvarying voltages. Moreover thismethodimplies the necessity of providing a negative bias to thesuppressor grid, which is a drawback in many cases. g,

According'to the present invention, it is possible to use in this case amulti-grid tube such as a hexode or a tube having a number of gridshigher than that generally used in frequency changing'tubes. 1

The unmodulatedj impulse is applied to one of the control grids, say thefirst grid while the modulating voltage is applied to the second orcontrol grid.

Accompanying drawings show respectively in Figs. 1 and 2 two embodimentsof our invention given by way of example and by no means in a bindingsense.

voltage; it may for instance be connected for this purpose with thecathode. The source of unmodulated impulses is shown at 2 and theimpulses are fed to the first grid through the condenser 3, said gridbeing grounded through the The impulses are applied, here resistance 4again in their positive direction. Their amplitudeis at least equaltothe cut off voltage of the tube that is to the absolute value of thenegative voltage that it is necessary to apply to said grid for cuttingoff the anode current of the tube.

A method in current use heretofore for produce 6 Claims. (Cl. 33264) 2The time constant of the system 3-4 is considerably higher than theduration separating two consecutive impulses fed by the source 2.

It is a known fact that under such conditions, the actionof "the gridcathode current is such that during the interval separating twoimpulses, the grid of the tube is brought to a value less than the cutgff value, said grid assuming a potential practically equal to that ofthe cathode at the moment of the passage of the impulses, this being theusual well known effect of peak'detectors. The consequence is that,whatever may be the amplitude of the pulses fed by the source '2provided they are higher than the above mentioned cut off voltage, thetube is locked between the impulses as the grid is brought to thepotential of the cathode onlyat the moment of the passage of theimpulses so as to release the tube at this moment and only at thismoment.

The modulating voltage pro-vided by the source of positive voltage 5which varies slightly as a function of time and that may reach the valuezero, is applied to the second controlling grid of the tube I so as toamplitude modulate the impulses produced by said tube as a function ofthe instantaneous voltage of said supply 5.

According to an important feature of our invention, an improvedlinearity of the impulses is obtained through a feedback system insertedbetween the supply 5 and the second controlling grid 6. This feedbackincludes a resistance I inserted between the source 5 and the grid 6 anda condenser 8 inserted between the anode 9 of the tube l and the pointconnecting the grid 6 with the resistance l.

H] designates the loadresistance inserted in the anode circuit, saidresistance being connected through its end opposed to the anode with ahigh voltage source that is not illustrated.

The impulses provided at the output of the tube l are supplied to theoutput circuit connected at a point between the anode 9 and theresistance II], to the terminals l! and I2.

The feedback arrangement described operates as follows:

The above disclosure shows that the tube is locked during the intervalsbetween the successive impulses and is capable of feeding current onlyat the moment of the passage of the latter.

At this moment the voltage at the point between the anode G and theresistor l0 drops suddenly by reason of the instantaneous drop in.voltage through the resistance Ill; this drop in the condenser B to thegrid 6 because theresistance I is of a high value compared to theinternal resistance of the source 5.

Calculation shows that if the product of the internal resistance of thetube I and the slope of the curve, giving the anode current of the tubeas a function of the variation in potential of the grid 6, issubstantially greater than 1, the voltage of the grid 5 at the moment ofthe passage of the impulse, which voltage is due both to the action ofthe resistance I and condenser 8 and to the voltage it has received fromthe source 5 immediately before, is such that the drop in voltage acrossthe resistance I is precisely equal to the value of the modulatingvoltage applied to the grid 6 at the moment of the arrival ,of theimpulse, in spite of the curvature of the characteristic curve of thetube. This provides an impulse that is a linear function of theinstantaneous modulation voltage provided by the source it is evenapparent that this linear function is reduced to equality. Consequentlyfor a zero voltage of the source 5, the impulse obtained is wiped out.

In order to avoid any substantial modification in the voltage of thegrid =6, while the impulse is being transmitted, the condenser 8 isgiven a sufficient capacity for the time constant of the system I8 to behigh with reference to the duration of said impulse.

An important application of the invention is that wherein severalsystems of the type illustrated in Fig. l are used, for providing amultiplex communication. The simplest manner of proceeding in this caseconsists in inserting several tubes in parallel with the common anodicresistance I0, said tubes receiving unmodulated impulses that arestaggered as to time and separated modulating voltages, whereby there iscollected across the terminals II---I2 the desired train of impulses,while a supplementary member may provide the synchronising impulse. Insuch an arrangement, the following drawback appears sage of an impulsethrough the tube considered,

the voltage of the grid 6 is not exactly that of the source 5 whichleads to cross-talk or interaction between the diil'erent channels ofthe multiplex communication system.

Fig. 2 shows a modification of the arrangement that removes thisdrawback. The elements already shown in Fig. 1 play the same part andhave received the same reference number. Thus the anodes of all thetubes such as I are connected in parallel with the lower end of theresistance I0.

Now according to a further feature of our invention, there is connectedbetween the resistance I0, common to all the tubes, and each of thetubes, such as I, a diode I3, the anode of which is connected to theresistance It and the cathode to theanode of the tube I. The condenser 8is connected to a point between the cathode of diode I3 and the anode oftube I. There is thus inserted in series with the high voltage anodesource, in addition to the resistance III and tube I, the diode I3. Byreason of the presence of such a diode, it is apparent that the negativeimpulses produced .in theresistance In by tubes '4 other than the tube Iconsidered, are without any action on the condenser 8 of said tube I asthe diode I3 prevents their passage. This removes completely the abovementioned drawback.

Obviously, the diode I3 .may be replaced by rectifiers and many otherdetails may also be changed without widening unduly the scope of ourpresent invention as defined in accompanying claims.

Our invention is applicable in particular to advantage to differentmeasuring systems operating through impulses.

What we claim is:

1. A mixing tube circuit adapted to provide amplitude modulationimpulses in linear relationship with modulating voltages, comprising amixing tube having a plurality of grids, means for feeding unmodulatedimpulses to one of said grids, means for feeding a modulating voltage toa second one of said grids and a feedback system coupling saidsecondgrid with the anode of said tube to produce the aforesaid linearrelationship.

2. A mixing tube circuit adapted to provide amplitude modulated impulsesin linear relationship with modulating voltages, comprising a tubehaving a plurality of grids, means for feeding unmodulated impulses toone of said grids, means for feeding a modulating voltage to a secondone of said grids and a feedback system coupling said second rid withthe anode of said tube, said feedback system including a resistance inseries with said last mentioned grid and a capacitor connected toprovide a connection between said last mentioned grid and said anode toproduce the aforesaid linear relationship.

3. In a mixing tub circuit adapted to provide amplitude modulatedimpulses in linear relationship with modulating voltages, comprising amixing tube having a first grid and a second grid and an anode, a sourceof unmodulated impulses, connections for connecting said source to saidfirst grid, said tube being biased to cutoff and the amplitude of saidimpulses being such as to overcome said bias and permit current to flowthrough said tube, a source of modulated impulses connected to saidsecond grid and a feedback system connected to the anode of said tubeand to said second grid, said feedback system comprising aresistor-capacitor circuithaving a time constant that is high comparedto the duration of the individual impulses of said second source, saidfeedback system functioning to produce a linear relationship between theamplitude modulated impulses in the output of said tube and the voltageof said modulated impulse source.

4. In a mixing tube circuit adapted to provide amplitude modulatedimpulses in linear relationship with modulating voltages, comprising amixing tube having a first grid and a second grid and an anode, a sourceof unmodulated impulses, a resistor-capacitor circuit having a timeconstant considerably greater than the duration separating twoconsecutive impulses of said source, connections for connectin saidresistor-capacitor circuit between said source and said first grid, saidtube being biased to cutoff and the amplitude of said impulses beingsuch as to overcome said bias and permit current to flow through saidtube, a source of modulated impulses connected to said second grid and afeedback system connected to the anode of said tube and to said secondgrid, said feedback system functioning to produce linear relationshipbetween the amplitude modulated impulses in the output of said tube andthe voltage of said modulated impulse source.

5. In a mixing tube circuit adapted to provide amplitude modulatedimpulses in linear relationship with modulating voltages, comprising amixing tube having a first grid and a second grid and an anode, a sourceof unmodulated impulses, a resistor-capacitor circuit havin a timeconstant considerably greater than the duration separating twoconsecutive impulses of said source, connections for connecting saidresistor-capacitor circuit between said source and said first grid, saidtube being biased to cutoff and the amplitude of said impulses beingsuch as to overcome said bias and permit current to flow through saidtube, a source of modulated impulses connected to said second grid and afeedback system connected to the anode of said tube and to said secondgrid,

said feedback system comprising a resistor-capacitor circuit having atime constant that is high compared to the duration of the individualimpulses of said second source, said feedback system functioning toproduce a linear relationship between the amplitude modulated impulsesin the output of said tube and the voltage of said modulated impulsesource.

6. In a mixing tube circuit adapted to provide amplitude modulatedimpulses in linear relation- JACQUES BOISVIEUX. JACQUES CHAUIMIERON.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 2,248,549 Schlesinger July 8,1941 2,278,159 Wheeler Mar. 31, 1942 2,462,111 Levy Feb. 22, 1949FOREIGN PATENTS Number Country Date 388,756 Great Britain Feb. 28, 1933

